Lower FNEG ( FABS (x) ) -> FNABS (x) [X86 codegen] PR20578

Negative FABS of either a scalar or vector should be handled the same way
on x86 with SSE/AVX: a single OR instruction of the FP operand with a
constant to light up the sign bit(s).

http://llvm.org/bugs/show_bug.cgi?id=20578

Differential Revision: http://reviews.llvm.org/D5201

llvm-svn: 218822

1 files changed, 77 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/fnabs.ll b/llvm/test/CodeGen/X86/fnabs.ll
new file mode 100644
index 00000000000..19718d3ff92
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fnabs.ll
@@ -0,0 +1,77 @@
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mcpu=corei7-avx| FileCheck %s
+
+; Verify that we generate a single OR instruction for a scalar, vec128, and vec256
+; FNABS(x) operation -> FNEG (FABS(x)).
+; If the FABS() result isn't used, the AND instruction should be eliminated.
+; PR20578: http://llvm.org/bugs/show_bug.cgi?id=20578
+
+define float @scalar_no_abs(float %a) {
+; CHECK-LABEL: scalar_no_abs:
+; CHECK: vorps
+; CHECK-NEXT: retq
+  %fabs = tail call float @fabsf(float %a) #1
+  %fsub = fsub float -0.0, %fabs
+  ret float %fsub
+}
+
+define float @scalar_uses_abs(float %a) {
+; CHECK-LABEL: scalar_uses_abs:
+; CHECK-DAG: vandps
+; CHECK-DAG: vorps
+; CHECK: vmulss
+; CHECK-NEXT: retq
+  %fabs = tail call float @fabsf(float %a) #1
+  %fsub = fsub float -0.0, %fabs
+  %fmul = fmul float %fsub, %fabs
+  ret float %fmul
+}
+
+define <4 x float> @vector128_no_abs(<4 x float> %a) {
+; CHECK-LABEL: vector128_no_abs:
+; CHECK: vorps
+; CHECK-NEXT: retq
+  %fabs = tail call <4 x float> @llvm.fabs.v4f32(< 4 x float> %a) #1
+  %fsub = fsub <4 x float> <float -0.0, float -0.0, float -0.0, float -0.0>, %fabs
+  ret <4 x float> %fsub
+}
+
+define <4 x float> @vector128_uses_abs(<4 x float> %a) {
+; CHECK-LABEL: vector128_uses_abs:
+; CHECK-DAG: vandps
+; CHECK-DAG: vorps
+; CHECK: vmulps
+; CHECK-NEXT: retq
+  %fabs = tail call <4 x float> @llvm.fabs.v4f32(<4 x float> %a) #1
+  %fsub = fsub <4 x float> <float -0.0, float -0.0, float -0.0, float -0.0>, %fabs
+  %fmul = fmul <4 x float> %fsub, %fabs
+  ret <4 x float> %fmul
+}
+
+define <8 x float> @vector256_no_abs(<8 x float> %a) {
+; CHECK-LABEL: vector256_no_abs:
+; CHECK: vorps
+; CHECK-NEXT: retq
+  %fabs = tail call <8 x float> @llvm.fabs.v8f32(< 8 x float> %a) #1
+  %fsub = fsub <8 x float> <float -0.0, float -0.0, float -0.0, float -0.0, float -0.0, float -0.0, float -0.0, float -0.0>, %fabs
+  ret <8 x float> %fsub
+}
+
+define <8 x float> @vector256_uses_abs(<8 x float> %a) {
+; CHECK-LABEL: vector256_uses_abs:
+; CHECK-DAG: vandps
+; CHECK-DAG: vorps
+; CHECK: vmulps
+; CHECK-NEXT: retq
+  %fabs = tail call <8 x float> @llvm.fabs.v8f32(<8 x float> %a) #1
+  %fsub = fsub <8 x float> <float -0.0, float -0.0, float -0.0, float -0.0, float -0.0, float -0.0, float -0.0, float -0.0>, %fabs
+  %fmul = fmul <8 x float> %fsub, %fabs
+  ret <8 x float> %fmul
+}
+
+declare <4 x float> @llvm.fabs.v4f32(<4 x float> %p)
+declare <8 x float> @llvm.fabs.v8f32(<8 x float> %p)
+
+declare float @fabsf(float)
+
+attributes #1 = { readnone }
+